Hi!
>AFAIK Excel won't pop up extra windows when instanciated via code. What
>I've ment is if you start Excel by hand, do you get any screens
>(activation, ...)? This was causing my problem.
Yes, this is also what I ment with "starting interactively" (->"by hand"): so unfortunately it does not pop up any screens, so there is not the reason.

>VSTO = Visual Studio Tools for Office and they are mainly used for writing
>add-in for Office - don't know if you intend to do so.
This time I didn't. Do you still think it could help me?